1. Field of the Invention
The present invention relates to a method of treating water to remove hardness and/or sulfate concentration.
The present day commercial processes reduce hardness by ion exchange in sodium, hydrogen cycle operation and "Desal Process" or the following softening reactions forming insoluble calcium carbonate and magnesium hydroxide: EQU Ca(HCO.sub.3).sub.2 + Ca(OH).sub.2 = 2 CaCO.sub.3 + H.sub.2 0 EQU caCl.sub.2 + Na.sub.2 CO.sub.3 = CaCO.sub.3 + 2 NaCl EQU CaSO.sub.4 + Na.sub.2 CO.sub.3 = CaCO.sub.3 + Na.sub.2 SO.sub.4 EQU mg (HCO.sub.3).sub.2 + 2 Ca(OH).sub.2 = Mg (OH).sub.2 + CaCO.sub.3 EQU mg Cl.sub.2 + Ca(OH).sub.2 + Na.sub.2 CO.sub.3 = Mg (OH).sub.2 + CaCO.sub.3 + 2 NaCl EQU Mg SO.sub.4 + Ca(OH).sub.2 +Na.sub.2 CO.sub.3 = Mg (OH).sub.2 + CaCO.sub.3 + Na.sub.2 SO.sub.4
it can be seen that only hardness associated with alkalinity is being removed without substituting sodium for hardness.
Sulfate is being removed from water in present day commercial processes by ion exchange, reverse osmosis, electrodialisis or by barium sulfate precipitation: EQU CaSO.sub.4 + BaCO.sub.3 = BaSO.sub.4 + CaCO.sub.3
reverse osmosis of acidic waste has been also applied, concentrating highly soluble calcium bisulfate followed by converting calcium bisulfate to less soluble calcium sulfate and consequent precipitation of calcium sulfate.
Calcium sulfate is a troublesome mineral in industrial water management as it restricts the reuse of water due to to its limited solubility, and tendency to scale or deposit within the industrial process and possibly downgrade the industrial process.
The concentration of calcium sulfate in an industrial process water is controlled by bleed-off from the system and applying softening reactions and processes described above, to facilitate further reuse of the waste stream.
The most advanced present day water management in evaporative cooling systems use sulfuric acid control scaling by calcium carbonate and softening reactions converting calcium sulfate to sodium sulfate. As there is no sulfate and sodium reduction in the reclamation, the concentration of dissolved solids increases due to evaporation to a point where the dissolved solids concentration must be controlled by bleedoff.
The amount of dissolved solids being bled from the system and particularly the amount of the sodium ion is greater than the amounts brought to the system with makeup water. This is a quite costly operation due to the costs of sodium carbonate and disposal of dissolved or soluble solids.